Flexible bag with vent for pressure release

ABSTRACT

A flexible bag having a reclosable zipper construction in which material is provided on the inside face of one or both zipper flanges that results in a weak seal area or an unsealed area when the side seals are made. The weak seal area or unsealed area is located on the product side of the zipper closure profiles. Elevated pressure inside the bag will cause the weak seal area of the side seal to fail as intended or will cause the zipper flanges in the unsealed area to separate, resulting in a venting action during cooking of the bag contents. For example, steam inside the bag can escape through the vent or vents while the zipper remains closed. Preferably the bag has a bottom gusset so that it can stand upright in a microwave oven. The bag may be opened to add contents, resealed and then heated.

RELATED PATENT APPLICATION

This application claims the benefit, under Title 35, United States Code,§119(e), of U.S. Provisional Application No. 61/056,691 filed on May 28,2008.

BACKGROUND

Historically, reclosable bags having press-to-close or slide-to-closereclosable feature were designed for food storage applications such asnon-refrigerated and refrigerated storage. These bag products weremanufactured from a combination of polyethylene resins with a reclosablefeature. More recently, such reclosable bag products have been designedfor high-temperature applications; for example, they are microwavable.

This invention relates to a flexible bag for use in the microwaving ofcookable items, and more specifically pertains to the controlled ventingof any pressure or steam generated within the bag during microwaving toassure that such is effectively released to the atmosphere.

Venting packages work well when the contents are pre-packaged, but inmany cases it may be desirable to add ingredients to the packagecontents just before heating. For example, one may wish to add spices tothe package contents prior to heating. There is a need for improvementsin reclosable bags or pouches designed for high-temperature applicationsthat will allow ingredients to be added to the package before cooking.

BRIEF SUMMARY

Disclosed herein are flexible bags having a reclosable zipperconstruction in which material is provided on the inside face of one orboth zipper flanges that results in a weak seal area or an unsealed areawhen the side seals are made. The weak seal area or unsealed area islocated on the product side of the zipper closure profiles. Elevatedpressure inside the bag will cause the weak seal area of the side sealto fail as intended or will cause the zipper flanges in the unsealedarea to separate, resulting in a venting action during cooking of thebag contents. For example, steam inside the bag can escape through thevent or vents while the zipper remains closed. Preferably the bag has abottom gusset so that it can stand upright in a microwave oven. The bagmay be opened to add contents, resealed and then heated. Many differentstyles of closure profiles can be incorporated into this design.

One aspect of the invention is a bag comprising a receptacle having amouth and an interior volume, and a reclosable structure installed inthe mouth of the receptacle. The receptacle comprises first and secondwalls that bound the interior volume and first and second side sealregions that include respective marginal portions of the first andsecond walls. The reclosable structure comprises first and second zipperstrips, the first zipper strip comprising a first base web attached tothe first wall and a first closure profile projecting from the firstbase web, and the second zipper strip comprising a second base webattached to the second wall and a second closure profile projecting fromthe second base web, the first and second closure profiles beingmutually interlockable. A first portion of the first base web is weaklysealed to a first portion of the second base web in a weak seal area ofthe first side seal region, and a second portion of the first base webis weakly sealed to a second portion of the second base web in a weakseal area of the second side seal region. The first portions of thefirst and second base webs in the first weak seal area have a sealstrength such that the first portions of the first and second base webswill separate from each other, thereby forming a vent, when the pressureinside the interior volume of the receptacle increases to a sufficientlevel, thereby allowing gas to escape from the interior volume into theambient atmosphere via the vent during cooking of product containedwithin the interior volume of the receptacle while the mouth of thereceptacle is in a fully closed state.

Another aspect of the invention is a bag comprising a receptacle havinga mouth and an interior volume, and a reclosable structure installed inthe mouth of the receptacle. The receptacle comprises first and secondwalls that bound the interior volume and first and second side sealregions that include respective marginal portions of the first andsecond walls. The reclosable structure comprises first and second zipperstrips, the first zipper strip comprising a first base web attached tothe first wall and a first closure profile projecting from the firstbase web, and the second zipper strip comprising a second base webattached to the second wall and a second closure profile projecting fromthe second base web, the first and second closure profiles beingmutually interlockable. A first portion of the first base web is notsealed to a first portion of the second base web in a portion of thefirst side seal region, and a second portion of the first base web isnot sealed to a second portion of the second base web in a portion ofthe second side seal region. The first portions of the first and secondbase webs form a vent when the pressure inside the interior volume ofthe receptacle increases to a sufficient level, thereby allowing gas toescape from the interior volume into the ambient atmosphere via the ventduring cooking of product contained within the interior volume of thereceptacle while the mouth of the receptacle is in a fully closed state.

A further aspect of the invention is a bag comprising a receptaclehaving a mouth and an interior volume, and a reclosable structureinstalled in the mouth of the receptacle. The receptacle comprises firstand second walls that bound the interior volume and first and secondside seal regions that include respective marginal portions of the firstand second walls. The reclosable structure comprises first and secondextruded plastic zipper strips, the first zipper strip comprising afirst base web attached to the first wall and a first closure profileprojecting from the first base web, and the second zipper stripcomprising a second base web attached to the second wall and a secondclosure profile projecting from the second base web, the first andsecond closure profiles being mutually interlockable. Prior to formationof the first and second side seal regions, the first base web compriseda band-shaped surface area which extended the entire length of a face ofthe first base web, the band-shaped surface area being made of a firstresin that forms a weak seal area with an opposing surface area made ofa second resin different than said first resin during formation of thefirst side seal region.

Other aspects of the invention are disclosed and claimed below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing showing a plan view of a reclosable bag inaccordance with a first embodiment.

FIG. 2 is a drawing showing a sectional view of one upper portion of thebag depicted in FIG. 1, the section being taken along line 2-2 seen inFIG. 1.

FIG. 3 is a drawing showing a sectional view of another upper portion ofthe bag depicted in FIG. 1, the section being taken along line 3-3 seenin FIG. 1.

FIG. 4 is a drawing showing the same sectional view as that seen in FIG.3, except that opposing portions of the zipper base webs in a weak sealarea are shown in an unsealed and separated state, thereby forming avent that is in flow communication with the interior volume of the bag.

FIG. 5 is a drawing showing a sectional view of a mouth portion of a bagin accordance with a second embodiment.

FIG. 6 is a drawing showing a sectional view of a side seal portion of abag in accordance with the second embodiment.

FIG. 7 is a drawing showing the same sectional view as that seen in FIG.6, except that opposing portions of the zipper base webs in a weak sealarea are shown in an unsealed and separated state, thereby forming avent that is in flow communication with the interior volume of the bag.

FIG. 8 is a drawing showing a sectional view of a mouth portion of a bagin accordance with a third embodiment.

FIG. 9 is a drawing showing a sectional view of a side seal portion of abag in accordance with the third embodiment.

FIG. 10 is a drawing showing the same sectional view as that seen inFIG. 9, except that opposing unsealed portions of the zipper base websare shown separated, thereby forming a vent that is in flowcommunication with the interior volume of the bag.

FIG. 11 is a drawing showing a sectional view of a side seal portion ofa bag in accordance with a fourth embodiment.

Reference will hereinafter be made to the drawings in which similarelements in different drawings bear the same reference numerals.

DETAILED DESCRIPTION

The vented reclosable bags disclosed herein are designed to withstandthe particular temperature and pressure conditions attending microwavecooking. Each reclosable bag is made of flexible material, such aspolypropylene, plastic lamination films or otherhigh-melting-temperature flexible material. Each reclosable bag has areclosable structure, e.g., a zipper comprising a pair of extrudedplastic zipper strips having mutually interlockable closure profiles.The zipper has a construction which allows the formation of one or morevents for pressure relief during cooking of the bag contents. The ventsare located on the product side of the zipper closure profiles at theside edges of the bag. Optionally, the bag may be constructed with abottom gusset that enables the bag to stand upright inside a microwaveoven. For each embodiment disclosed hereinafter, the plastic film usedto construct the bag may be thin for single-use bags or thick formultiple-use bags.

The reclosable structure remains closed as the pressure inside the bagincreases during cooking. For example, the bag and its contents may beplaced inside a microwave oven, which oven is then set to cook the bagcontents. During this process, the pressure buildup inside the bag isrelieved by the release of steam through the one or more vents formed inthe reclosable bag. The pressure relief prevents the bag from burstingor otherwise having its integrity compromised.

FIGS. 1-4 depict one embodiment of a high-temperature reclosable bagsuitable for use in cooking food. The bag shown in FIG. 1 comprises areceptacle 2 made of flexible material, such as polypropylene film,plastic lamination film, other higher-melting-temperature material, or acombination of two or more of the foregoing types of flexible material.A web of flexible high-temperature material is folded web to form afront panel 4, a rear panel (not shown in FIG. 1) and a bottom gusset 8and then heat sealed (or ultrasonically welded) in marginal regionsadjacent the top edges and the side edges of the folded web. The sideseals are indicated by hatched regions 16 and 18 in FIG. 1. The top sealis not indicated in FIG. 1, but would include marginal portions at thetop edges of the front and rear panels, as is well known in the art. Theresulting receptacle 2 has an interior volume (not shown) for foodproduct and a mouth in which a reclosable plastic zipper 10 havingflanges is installed. In this embodiment, the zipper 10 comprises twozipper strips having mutually interlockable closure profiles 22 and 24projecting from respective base webs 12 and 14 that are joined to thefront and rear bag panels (hereinafter “walls”) 4 and 6, respectively,as seen in the sectional view presented in FIG. 2. These base webs arejoined to the bag walls by heat sealing or ultrasonic welding and extendacross the mouth of the receptacle from one side seal 16 to the otherside seal 18 (indicated by hatching in FIG. 1).

The construction of the side seals 16 and 18 varies in an elevationaldirection. In the portions of the side seal regions disposed above thehorizontal dashed line 8 (which indicates the apex of the bottom gusset)seen in FIG. 1, respective confronting marginal portions of the frontand rear panels of the receptacle are sealed together except where theends of the base webs of zipper 10 intervene. The ends of the zipperbase webs are also joined together in the side seals 16 and 18, with theadjoining marginal portions of the front and rear panels being joined tothe fused zipper ends. Below the horizontal dashed line 8, respectivemarginal portions of the front panel and rear panels of the receptacleand intervening marginal portions of the two panels of the bottom gussetare all sealed together in the side seals 16 and 18.

Still referring to FIG. 1, the side seals 16 and 18 also includesrespective areas 20 and 20′ (located below the closure profiles) wherethe zipper base webs are weakly sealed together. This can beaccomplished by producing a zipper in which each base web has coextrudedmaterial on its inside face. FIG. 2 shows a sectional view of an upperportion of the reclosable bag depicted in FIG. 1, the section beingtaken along line 2-2 seen in FIG. 1, which is located away from the sideseals. As seen in the sectional view of FIG. 2, the base web 12 hascoextruded material 26 on its inside face, while the base web 14 hascoextruded material 28 on its inside face. This coextruded materialextends along the entire length of each base web.

The coextruded materials 26 and 28 may be the same or dissimilar. Ineither case, the coextruded materials are different than the resinmaterial of the remainder of the zipper (hereinafter “base resin”). Thematerials are selected so that when the side seals are formed, e.g., bythe application of heat and pressure, the coextruded materials 26 and 28will form a weak or minimal seal, whereas the base resin of therespective zipper strips will form a strong permanent seal in areasabove and below the weak seal.

FIG. 3 shows a sectional view of another upper portion of the bagdepicted in FIG. 1, the section being taken along line 3-3 seen in FIG.1, which is located in side seal region 18. A person skilled in the artof manufacturing reclosable packaging will appreciate that the zipperclosure profiles will be substantially deformed, i.e., crushed, in theside seal regions, which crushed profiles become part of the side seal,as seen in FIG. 3. At the time when the bag is produced, the coextrusionmaterial 26 and 28 is heat sealed and forms a sufficient bond such thatthe bag is sealed to form a weak seal area in the side seal region belowthe closure profiles.

When the package (i.e., bag with food contents) is placed in a microwaveoven and heated, internal pressure builds up. The closure profiles 22and 24 (see FIG. 2) can be made to stay closed when subjected to thisincrease in internal pressure. As the internal pressure continues toincrease, one or both of the two weak seals (e.g., weak seal 20′ seen inFIG. 3) at the side seals of the bag open up, allowing steam to escapefrom the interior volume of the receptacle, thereby relieving thepackage internal pressure. FIG. 4 shows the same sectional view as thatseen in FIG. 3, except that opposing portions of the zipper base webs inweak seal area 20′ are shown in an unsealed and separated state, therebyforming a vent 30 that is in flow communication with the interior volumeof the bag.

In accordance with the embodiment depicted in FIGS. 2-4, the coextrudedmaterials 26 and 28 are disposed on opposing inside faces of the basewebs 12 and 14 respectively. Both coextrusions could be a peel sealresin designed to form a peel seal when heat and pressure are appliedduring bag manufacture and to open later when the bag internal pressurereaches a desired level during cooking. The zipper strips and bag aretypically made of polyethylene-based materials. In instances where thebag material is a laminate film, the film surface that the zipper (madeof polyethylene-based material) seals to is typically also apolyethylene-based material.

Exemplary polyethylene-based materials that could be used as the zipperbase resin include, but are not limited to: high-density polyethylene(HDPE); medium-density polyethylene (MDPE); low-density polyethylene(LDPE); linear low-density polyethylene (LLDPE); cyclic olefincopolymers (a commercial example is Ticona's TOPAS resin); andcombinations of the foregoing. Polyethylene-based materials that couldbe used as base resins, but more likely would be used in combinationwith the base resins identified in the preceding sentence, include, butare not limited to, ultra-low-density polyethylene (ULDPE); verylow-density polyethylene (VLDPE); elastomers; plastomers;metallocene-catalyzed polyethylene; and combinations of the foregoing.

For polyethylene-based base resins, the coextrusions could be a resinthat has a higher seal initiation temperature than that of theparticular polyethylene-based material from which the zipper is made.Examples of such resins include polypropylene-based material orpolyester-based material. In accordance with further alternatives, thecoextruded material 26 can be different than the coextruded material 28.For example, coextruded material 26 could be a peel seal resin whilecoextruded material 28 could be a resin, such as a polypropylene-basedmaterial, having a higher seal initiation temperature than that ofpolyethylene-based material used as the base resin.

As used in the preceding paragraph and hereinafter, the term“polypropylene-based materials” includes, but is not limited to:polypropylene homopolymers; polypropylene copolymers; ethylene/propylenecopolymers; metallocene-catalyzed polypropylene; polypropylene-basedelastomers; and combinations of the foregoing.

In accordance with a further embodiment depicted in FIGS. 5-7, a weakseal area can be formed in each side seal by coextruding a layer 32material on the inner face of only one of the two base webs of thezipper, e.g., on base web 12 as shown in FIG. 5. In the case where thezipper strips and the bag material are made of polyethylene-basedmaterials, the coextrusion 32 could be a peel seal resin or a resin thatdoes not seal well to the particular polyethylene-based base resin, suchas a polypropylene-based material. In the case where the zipper stripsand the bag material are made of a polypropylene-based material, thecoextrusion could be a peel seal resin or a resin that does not sealwell to the particular polypropylene-based base resin, such as apolyethylene-based material. Alternatively, in both of the foregoingcases, the coextrusion 32 could be a biodegradable resin such aspolylactic acid or a polyhydroxyalkanoate. The result, shown in FIG. 6,is a weakly sealed area 20′ in the side seal 18, which weakly sealedarea will open, as shown in FIG. 7, when the bag internal pressurereaches a desired level during cooking.

Typical peel seal resins that could be used are DuPont Appeel 11D542 andBasell PB8640. Any of the various grades of resin sold for peelable filmor lidstock could also be used.

In accordance with another embodiment depicted in FIGS. 8-10, a vent canbe formed in each side seal by applying a coating 34 of heat-resistantmaterial, such as nitrocellulose, on the inner face of one of the twobase webs of the zipper, e.g., on base web 12, as shown in FIG. 8. Theheat-resistant coating is preferably applied on the inner face of baseweb 12 at least in the areas of the side seals. This technique can beapplied in both the case where the zipper strips and the bag materialare made of polyethylene-based materials and the case where the zipperstrips and the bag material are made of polypropylene-based materials.The presence of a heat-resistant material on a zipper base web in theside seal region prevents the coated base web from being heat sealed tothe confronting base web in the side seal region, thereby forming a ventthat opens in response to a sufficient pressure increase inside thereceptacle. FIG. 9 shows the vent 30 in a closed state; FIG. 10 showsthe vent 30 in an open state. In the alternative, both base webs canhave confronting portions which are coated with a heat-resistantmaterial.

In accordance with alternative embodiments, the pressure-release areacan be located above the closure profiles, i.e., on the consumer side ofthe profiles rather than on the product side. Such embodiments wouldhave utility in cases where the unopened bag filled with product is soldwith the zipper open. In this case the weakly sealed or unsealed area inthe side seal could be above or below the closure profiles of the openzipper.

FIG. 11 is a sectional view, taken through the side seal, of anembodiment wherein a weak seal area has been formed in the side seal bycoextruding a layer 32 material on the inner face of base web 12 at anelevation higher than the elevation of the closure profiles. In the casewhere the zipper strips and the bag material are made ofpolyethylene-based materials, the coextrusion 32 could be a peel sealresin or a resin that does not seal well to the particularpolyethylene-based base resin, such as a polypropylene-based material.In the case where the zipper strips and the bag material are made of apolypropylene-based material, the coextrusion could be a peel seal resinor a resin that does not seal well to the particular polypropylene-basedbase resin, such as a polyethylene-based material. Alternatively, inboth of the foregoing cases, the coextrusion 32 could be a biodegradableresin of a type previously described. Any of the various grades of resinsold for peelable film or lidstock could also be used.

In accordance with further alternative embodiments, a weak seal area ora vent can be formed in a side seal region at the interface of a zipperflange and a confronting portion of the bag wall. For example, theembodiment depicted in FIGS. 5-7 could be altered by placing thecoextrusion 32 on the outside face of the lower zipper flange ratherthan on the inside face. Similarly, the embodiment depicted in FIGS.8-10 could be altered by placing the coating 34 on the outside face ofthe lower zipper flange rather than on the inside face. In addition, theembodiment depicted in FIG. 10 could be altered by placing thecoextrusion 32 on the outside face of the upper zipper flange ratherthan on the inside face.

With respect to all embodiments disclosed above, a person skilled in theart will appreciate that the broad scope of the invention includesreclosable bags having only one vent as well as bags having two or morevents.

While the invention has been described with reference to preferredembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted formembers thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationto the teachings of the invention without departing from the essentialscope thereof. Therefore it is intended that the invention not belimited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A bag comprising a receptacle having a mouth and an interior volume,and a reclosable structure installed in said mouth of said receptacle,said receptacle comprising first and second walls that bound saidinterior volume and first and second side seal regions that includerespective marginal portions of said first and second walls, saidreclosable structure comprising first and second zipper strips, saidfirst zipper strip comprising a first base web attached to said firstwall and a first closure profile projecting from said first base web,and said second zipper strip comprising a second base web attached tosaid second wall and a second closure profile projecting from saidsecond base web, said first and second closure profiles being mutuallyinterlockable, wherein a first portion of said first base web is weaklysealed to a first portion of said second base web in a weak seal area ofsaid first side seal region, and a second portion of said first base webis weakly sealed to a second portion of said second base web in a weakseal area of said second side seal region, said first portions of saidfirst and second base webs in said first weak seal area having a sealstrength such that said first portions of said first and second basewebs will separate from each other, thereby forming a vent, when thepressure inside said interior volume of said receptacle increases to asufficient level, thereby allowing gas to escape from said interiorvolume into the ambient atmosphere via said vent during cooking ofproduct contained within said interior volume of said receptacle whilesaid mouth of said receptacle is in a fully closed state.
 2. The bag asrecited in claim 1, wherein said first portion of said first base web insaid weak seal area of said first side seal region comprises a layer ofa first resin, and a second portion of said first base web adjacent saidfirst portion of said first base web and not in said weak seal area ofsaid first side seal region is made of a second resin different thansaid first resin.
 3. The bag as recited in claim 2, wherein said secondresin is a polyethylene-based material and said first resin is selectedfrom a group of resins which do not seal well to that polyethylene-basedmaterial.
 4. The bag as recited in claim 3, wherein said first resin isa polypropylene-based material or a polyester-based material.
 5. The bagas recited in claim 2, wherein said second resin is apolypropylene-based material and said first resin is selected from agroup of resins which do not seal well to that polypropylene-basedmaterial.
 6. The bag as recited in claim 5, wherein said first resin isa polyethylene-based material.
 7. The bag as recited in claim 2, whereinsaid first resin is a biodegradable resin such as polylactic acid or apolyhydroxyalkanoate.
 8. The bag as recited in claim 2, wherein saidfirst resin is a peel seal resin.
 9. The bag as recited in claim 2,wherein said first portion of said second base web in said weak sealarea of said first side seal region comprises a layer of a third resindifferent than said first and second resins, and a second portion ofsaid second base web adjacent said first portion of said first base weband not in said weak seal area of said first side seal region is made ofsaid second resin.
 10. A bag comprising a receptacle having a mouth andan interior volume, and a reclosable structure installed in said mouthof said receptacle, said receptacle comprising first and second wallsthat bound said interior volume and first and second side seal regionsthat include respective marginal portions of said first and secondwalls, said reclosable structure comprising first and second zipperstrips, said first zipper strip comprising a first base web attached tosaid first wall and a first closure profile projecting from said firstbase web, and said second zipper strip comprising a second base webattached to said second wall and a second closure profile projectingfrom said second base web, said first and second closure profiles beingmutually interlockable, wherein a first portion of said first base webis not sealed to a first portion of said second base web in a portion ofsaid first side seal region, and a second portion of said first base webis not sealed to a second portion of said second base web in a portionof said second side seal region, said first portions of said first andsecond base webs forming a vent when the pressure inside said interiorvolume of said receptacle increases to a sufficient level, therebyallowing gas to escape from said interior volume into the ambientatmosphere via said vent during cooking of product contained within saidinterior volume of said receptacle while said mouth of said receptacleis in a fully closed state.
 11. The bag as recited in claim 10, whereinsaid first portion of said first base web is coated with aheat-resistant material.
 12. The bag as recited in claim 11, whereinsaid heat-resistant material is nitrocellulose.
 13. A bag comprising areceptacle having a mouth and an interior volume, and a reclosablestructure installed in said mouth of said receptacle, said receptaclecomprising first and second walls that bound said interior volume andfirst and second side seal regions that include respective marginalportions of said first and second walls, said reclosable structurecomprising first and second extruded plastic zipper strips, said firstzipper strip comprising a first base web attached to said first wall anda first closure profile projecting from said first base web, and saidsecond zipper strip comprising a second base web attached to said secondwall and a second closure profile projecting from said second base web,said first and second closure profiles being mutually interlockable,wherein prior to formation of said first and second side seal regions,said first base web comprised a band-shaped surface area which extendedthe entire length of a face of said first base web, said band-shapedsurface area being made of a first resin that forms a weak seal areawith an opposing surface area made of a second resin different than saidfirst resin during formation of said first side seal region.
 14. The bagas recited in claim 13, wherein said second resin is apolyethylene-based material and said first resin is selected from agroup of resins which do not seal well to that polyethylene-basedmaterial.
 15. The bag as recited in claim 14, wherein said first resinis a polypropylene-based material or a polyester-based material.
 16. Thebag as recited in claim 13, wherein said second resin is apolypropylene-based material and said first resin is selected from agroup of resins which do not seal well to that polypropylene-basedmaterial.
 17. The bag as recited in claim 16, wherein said first resinis a polyethylene-based material.
 18. The bag as recited in claim 13,wherein said first resin is a biodegradable resin such as polylacticacid or a polyhydroxyalkanoate.
 19. The bag as recited in claim 13,wherein said first resin is a peel seal resin.
 20. The bag as recited inclaim 13, wherein said first resin is totally resistant to heat sealing.